Microfluidic devices, such as ‘lab on a disc’ devices allow the sequencing and control of small volumes of liquid through conduits and chambers on the scale of micrometers to millimeters. Liquid may be caused to flow through such a microfluidic device under the action of centrifugal force, by rotating the device and controlling the frequency of rotation. Other options for inducing flow of a liquid through a microfluidic device include pressure-driven flow and capillary driven flow.
In the case of capillary driven flow, a way of ensuring that liquid flows through the required parts of the device is to narrow a flow path one or more times along its extent, as described in application EP13708496.8, incorporated herein by reference in its entirety. Capillary forces acting on a liquid in a conduit are greater the narrower the conduit and sequential narrowing of the flow path maintains capillary driven flow in the face of hydraulic resistance. Narrowing may be achieved by a reduction in depth of a conduit, by a reduction in width of a conduit, or both. The present application focuses on the situation in which a first conduit with a first depth is joined to a second conduit with a depth less than that of the first conduit in order to advance a liquid from the first conduit to the second by capillary effect.